GRL

The Asian Monsoonal rainfall accounts for the majority of annual regional precipitation in East and South Asia and could be remotely regulated by El Niño-Southern Oscillation (ENSO). Besides, several paleoclimate records and simulations have indicated solar signals in the Asian Monsoon, implying the impact of solar activity on the regional monsoon precipitation. By conducting multi-linear regression analysis to the solar irradiance forced single-forcing experiment in the last millennium, this study presents the comparison of solar and ENSO effects on monsoonal precipitation in South and East Asia during early summer (May–June). Increased total solar irradiance during high solar activity years tends to trigger a favorable environment for developing monsoon onset, leading to more precipitation against ENSO-related patterns over Southeast and South Asia before peak-summer (July–August). The result supports reconstructed terrestrial records and underlines considerable influences of the solar cycle on the variation of the Asian Summer Monsoon.

This study examines the impact of ocean advection and surface freshwater flux on the non-seasonal, upper-ocean salinity variability in two climate model simulations with eddy-resolving and eddy-parameterized ocean components (HR and LR, respectively). We assess the realism of each simulation by comparing their sea surface salinity (SSS) variance with satellite and Argo float estimates. In the extratropics, the HR variance is about five times larger than that in LR and agrees with Argo. In turn, the extratropical satellite SSS variance is smaller than that from HR and Argo by about a factor of two, potentially caused by the insufficient resolution of radiometers to capture mesoscale features and their low sensitivity to SSS in cold waters. Using a simplified salinity conservation equation for the upper-50-m ocean, we find that the advection-driven variance in HR is, on average, 10 times larger than the surface flux-driven variance, reflecting the action of mesoscale processes.

Sulfate aerosol greatly contributes to wintertime haze pollution in emission-intensive regions like the North China Plain (NCP) in China. Fast sulfate increase and accumulation are usually recorded during winter haze; however, the multiphase oxidation of sulfur dioxide (SO2) and the physical processes affecting near-surface sulfate are not fully understood. By combining in situ observations and numerical simulations, we found that high sulfur oxidation ratios (>0.6) under heavily polluted conditions are associated with low clouds and fog over NCP, induced by the moist southerly airflow. Thick low clouds and high SO2 levels in NCP provide a reaction environment for sulfate production. The sulfate production rate in cloud water can reach 0.5–1.3 μg m−3 h−1. The results demonstrate that the vertical mixing of sulfate generated within the cloud water to the surface plays a significant role in rapid sulfate production, highlighting the importance of understanding cloud-water processes in haze pollution.

In some areas of Antarctica, blue-colored bare ice is exposed at the surface. These blue ice areas (BIAs) can trap meteorites or old ice and are vital for understanding the climatic history. By combining multi-sensor remote sensing data (MODIS, RADARSAT-2, and TanDEM-X) in a deep learning framework, we map blue ice across the continent at 200-m resolution. We use a novel methodology for image segmentation with “noisy” labels to learn an underlying “clean” pattern with a neural network. In total, BIAs cover ca. 140,000 km2 (∼1%) of Antarctica, of which nearly 50% located within 20 km of the grounding line. There, the low albedo of blue ice enhances melt-water production and its mapping is crucial for mass balance studies that determine the stability of the ice sheet. Moreover, the map provides input for fieldwork missions and can act as constraint for other geophysical mapping efforts.

We show that ModE-Sim, a global ensemble of atmospheric model simulations that uses observed ocean boundary conditions and radiative forcings providing 36 members with daily climate information can be used to in-depth analyze the known spatial and temporal variability of heatwaves in the Northern Hemisphere and Australia during the past 160 years. It can also be used to study actual past extreme events like heatwaves during the El Nino 1877/1878. To analyze past heatwaves we use a novel approach of a transient baseline climatology and compare to different observational data sets. Furthermore, we analyze sea surface temperature anomalies during the most extreme heatwave summers in North America, Europe and Australia and identify the most prominent anomaly patterns over the Subpolar North Atlantic and in the Central Pacific. Using a large ensemble of forced simulations, like ModE-Sim can consequently contribute to a better understanding of preindustrial heatwaves, their decadal variability and their driving mechanisms.

Aerosol water affects the physicochemical properties and mass concentration of organic aerosols (OA), but it is typically omitted by air quality, weather, and climate models. We compare two classes of simplified models to estimate the OA water uptake and gas–particle partitioning of organic compounds. One class uses a single-hygroscopicity-parameter (κ) approach while the other is based on the reduced-complexity Binary Activity Thermodynamics (BAT) model. We show that a BAT-based two-dimensional volatility basis set (VBS) model always predicts a higher OA mass concentration at elevated relative humidity (RH), for example, ∼16% at 80% RH, than any variation of the κ-based method considered—even when BAT-VBS predicts a lower water uptake. The main reason being that the BAT-VBS model captures variations in effective saturation mass concentration of organics (C*) with RH, a feature that other VBS methods lack. The BAT-VBS framework offers an efficient, RH-sensitive treatment for reduced-complexity OA modeling.

Melting of ice shelves can energize a wide range of ocean currents, from three-dimensional turbulence to relatively large-scale boundary currents. Here, we conduct high-resolution simulations of the western Amundsen Sea to show that submesoscale eddies are prevalent inside ice shelf cavities. The simulations indicate energetic submesoscale eddies at the top and bottom ocean boundary layers, regions with sharp topographic slopes and strong lateral buoyancy gradients. These eddies play a substantial role in the vertical and lateral (along-isopycnal) heat advection toward the ice shelf base, enhancing the basal melting in all simulated cavities. In turn, the meltwater provides strong buoyancy gradients that energize the submesoscale variability, forming a positive loop that could affect the overall efficiency of heat exchange between the ocean and the ice shelf cavity. Our study implies that submesoscale-induced enhancement of basal melting may be a ubiquitous process that needs to be parameterized in coarse-resolution climate models.

CIRBE (Colorado Inner Radiation Belt Experiment), a 3U CubeSat, was launched on 15 April 2023 into a sun synchronous orbit (97.4° inclination and 509 km altitude). The sole science payload onboard is REPTile-2 (Relativistic Electron and Proton Telescope integrated little experiment—2), an advanced version of REPTile which operated in space between 2012 and 2014. REPTile-2 has 60 channels for electrons (0.25–6 MeV) and 60 channels for protons (6.5–100 MeV). It has been working well, capturing detailed dynamics of the radiation belt electrons, including several orders of magnitude enhancements of the outer belt electrons after an intense magnetic storm, multiple “wisps”- an electron precipitation phenomenon associated with human-made very low frequency (VLF) waves in the inner belt, and “drift echoes” of 0.25–1.4 MeV electrons across the entire inner belt and part of the outer belt. These new observations provide opportunities to test the understanding of the physical mechanisms responsible for these features.

Carbonate sediments transported into the mantle at subduction zone settings account for the majority of the carbon flux into the Earth's interior and are thus critical to the deep carbon cycle. Understanding carbon storage volumes in the deep earth requires knowledge of the degree to which carbonate sediments are stored in the arc lithosphere or descend to the deep mantle. Here, we use petrological-thermomechanical modeling to indicate that solid-state diapirs dominate the removal of carbon from subducting plates, which may be the principal carbon-release mechanism for the Cyclades (Greece) and Costa Rican forearcs. We find that forearc diapirs remove up to ∼80% of subducting carbon and develop diagonally upward, resulting in massive carbon storage in the subarc lithosphere. Outgassing from the carbon storage may cause high carbon outputs and explain volcanic gas with high δ13C at some subduction zones, affecting atmospheric CO2 concentration.

The inflow of warm and salty Circumpolar Deep Water affects the melting of the ice shelf on the Amundsen Sea, a significant contributor to global sea level rise. Multi-year mooring data (2014–2016 and 2018–2020) from the front of the Dotson Ice Shelf show the modified Circumpolar Deep Water layer was thicker during 2018–2020 than during 2014–2016. During 2014–2016, Ocean surface stress curl influenced the barotropic process and strengthened southward velocity, while during 2018–2020, it caused lift and downwelling of thermocline depth, increasing the impact of the baroclinic process in ocean circulation. The heat transport to the ice shelf during 2018–2020 (57.42 MW m−1) was half as much as it was during 2014–2016 (111.06 MW m−1) due to a weaker lower layer current. The difference in ocean circulation between two periods, caused by a difference in warm layer thickness, ultimately impacts the heat transport entering the ice shelf cavity.

While the prominent influence of El Niño-Southern Oscillation (ENSO) on the Indian Ocean Oscillation (IOD) is widely recognized, intricate relationships between them are often invoked that introduce challenges into seasonal predictions. Previous studies have shown that different flavors of El Niño exhibit distinct associations with the IOD. In this study, we demonstrate that La Niña's teleconnection to the IOD is primarily controlled by its longitudinal position. Westward-displaced La Niña events tend to produce stronger negative convection anomalies in the central Pacific and more pronounced Walk Circulation anomalies, thereby triggering strong negative IOD events. In contrast, eastward-displaced La Niña events are usually accompanied by feeble convection response due to the excessively cold conditions in the cold tongue, yielding insignificant IOD response. The pivotal role of La Niña's longitudinal position on the IOD's response is realistically reproduced by targeted pacemaker experiments, providing new insights into inter-basin climate connections.

The cold Eurasia has been proposed to be closely linked to the weakening of the stratospheric polar vortex (SPV), however, how the Arctic sea ice modulates the surface impacts of the weak SPV is unclear. This study explores the critical modulating role of reduced Arctic sea ice in the surface cooling response to SPV stretching events in autumn. Here, through ERA5 reanalysis and Whole Atmosphere Community Climate Model simulations, we show that Eurasian cold events are more likely (45%) to occur in days 30–50 after the onset of SPV stretching events under lower Barents-Kara Seas (BKS) sea ice conditions, in contrast to under heavy BKS sea ice conditions when robust surface cooling is absent. The stratospheric and tropospheric pathways explain 46.8% and 53.2% of the total variance of Siberian coldness, respectively. The downward extension of anomalous stratospheric wave-2 ridge to the troposphere intensifies the Arctic-North European high, favoring the subsequent colder Siberia.

Aerosol measurements during the DOE ARM Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign were used to quantify the differences between clean and smoky cloud condensation nuclei (CCN) budgets. Accumulation-mode particles accounted for ∼70% of CCN at supersaturations <0.3% in clean and smoky conditions. Aitken-mode particles contributed <20% and sea-spray-mode particles <10% at supersaturations <0.3%, but at supersaturations >0.3% Aitken particles contributions increased to 30%–40% of clean CCN. For clean conditions, the Hoppel minimum diameter was correlated to the accumulation-mode number concentration, indicating aerosol-correlated cloud activation was controlling the lower diameter cutoff for which particles serve as CCN. For smoky conditions, the contributions of Aitken particles increase and the correlation of cloud activation to accumulation-mode particles is masked by the lower-hygroscopicity smoke. These results provide the first multi-month in situ quantitative constraints on the role of aerosol number size distributions in controlling cloud activation in the tropical Atlantic boundary layer.

The interior oceans of several icy moons are considered as affected by rotation. Observations suggest a larger heat transport around the poles than at the equator. Rotating Rayleigh-Bénard convection (RRBC) in planar configuration can show an enhanced heat transport compared to the non-rotating case within this “rotation-affected” regime. We investigate the potential for such a (polar) heat transport enhancement in these subglacial oceans by direct numerical simulations of RRBC in spherical geometry for Ra = 106 and 0.7 ≤ Pr ≤ 4.38. We find an enhancement up to 28% in the “polar tangent cylinder,” which is globally compensated by a reduced heat transport at low latitudes. As a result, the polar heat transport can exceed the equatorial by up to 50%. The enhancement is mostly insensitive to different radial gravity profiles, but decreases for thinner shells. In general, polar heat transport and its enhancement in spherical RRBC follow the same principles as in planar RRBC.

Future climate projections suggest a poleward shift of the maximum intensity of tropical cyclones (TCs) over the western North Pacific. However, the global nature of the latitudinal change in TC genesis under global warming remains poorly understood. We show, using large-ensemble high-resolution atmospheric model simulations (d4PDF) with four warming scenarios, that the poleward shift is a robust change over the globe, attributable to the weakening of the Hadley circulation. The weakened ascent driven by the upper-tropospheric warming suppresses the TC genesis within 5°–20° latitudes, whereas the weakened descent enhances the TC genesis in the poleward latitudes. We further estimate the poleward shift of TC genesis to emerge at the 2 K global warming over the Arabian Sea, South Atlantic and Pacific Oceans and at the 4 K warming over the North Pacific. The present results underscore the potential for increasing social and economic risks associated with TCs at higher latitudes.

The western North Pacific anticyclone (WNPAC) significantly influences the East Asian climate and is modulated by tropical sea surface temperature (SST). This study uses 142 AMIP simulations from 33 Coupled Model Intercomparison Project (CMIP6) models to quantify the contributions of SST to the interannual variability of the WNPAC. SST forcing accounts for 66%, 77%, and 49% of the WNPAC variance in winter, spring, and summer, respectively. The persistence of the WNPAC depends on the relaying effects of SST in three tropical oceans. CMIP6 models exhibit excessive precipitation response to the Pacific SST, leading to an overestimated (underestimated) Pacific (Indian Ocean) effect in modulating the summer WNPAC. Sensitivity experiments with an atmospheric model confirm the crucial role of the Pacific in regulating the WNPAC interannual variation and the contribution from the tropical North Atlantic in spring. The tropical Indian Ocean only exerts a minor impact on the WNPAC when excluding the interactions with other oceans.

Rare precipitation events with return periods of multiple decades to hundreds of years are particularly damaging to natural and societal systems. Projections of such rare, damaging precipitation events in the future climate are, however, subject to large inter-model variations. We show that a substantial portion of these differences can be ascribed to the projected warming uncertainty, and can be robustly reduced by using the warming observed during recent decades as an observational constraint, implemented either by directly constraining the projections with the observed warming or by conditioning them on constrained warming projections, as verified by extensive model-based cross-validation. The temperature constraint reduces >40% of the warming-induced uncertainty in the projected intensification of future rare daily precipitation events for a climate that is 2°C warmer than preindustrial across most regions. This uncertainty reduction together with validation of the reliability of the projections should permit more confident adaptation planning at regional levels.

We construct freshwater balance in the Bay of Bengal (BoB) within a control volume (CV) bounded by 1,018 kg/m3 isopycnal surface using observations and ocean reanalysis during 2011–2015. Freshwater in CV is maximum in October–November due to monsoonal rain and river inflows, and minimum in April–May. Water lighter than 1,018 kg/m3 is not transported out of BoB, implying that freshwater lost from CV is mixed away entirely within the basin. From freshwater budget, we infer moderate diapycnal mixing rates (∼0.8 × 10−5 m2/s) in boreal spring and summer; in winter (December–January), the rate of freshwater loss to subsurface ocean is 0.015 m/day, corresponding to a median turbulent diffusivity of 4.2 × 10−5 m2/s, with standard error of 25%. We show that enhanced winter mixing across the shallow pycnocline is due to reduced shortwave radiation and subseasonal episodes of surface buoyancy loss when cool, dry northeast monsoon winds blow over BoB.

A reliable projection of precipitation over the Tibetan Plateau (TP) is crucial for climate adaptation activities in this climate-sensitive region, but existing studies show a large spread in magnitude. Based on Coupled Model Intercomparison Project Phase 6 models, we investigate the TP summer precipitation projection and understand the sources of uncertainty. The results show that the TP exhibits a profound wetting trend throughout the 21st century, with precipitation increasing by 0.64 ± 0.06 mm day−1 during 2050–2099 under the SSP5–8.5 scenario. The moisture budget analysis indicates that the thermodynamical response to global warming determines the precipitation increase. However, both the thermodynamical and dynamical components contribute to the uncertainty of precipitation projection. The inter-model spread of the thermodynamic term arises from divergent global mean warming, which is closely related to model climate sensitivity. The uncertainty of the dynamic component is driven by model-dependent circulation changes induced by different equatorial Pacific warming rates.

Given sea ice's importance in global climate regulation, fully understanding the role of natural temperature and atmospheric patterns like the Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) in its variability is critical. While instrumental AMO and reliable AO records are available since the mid-1800s and 1958, respectively, satellite sea-ice concentration data sets start only in 1979, limiting the shared timespan to study their interplay. Growth increments of the coralline algae, Clathromorphum compactum, can provide sea-ice proxy information for years prior to 1979. We present a seasonal 210-year algal record from Lancaster Sound in the Canadian Arctic Archipelago capturing low frequency AMO/NAO variability and high frequency interannual AO/NAO prior to 2000. We suggest that sea-ice variability here is strongly coupled to these large-scale climate processes, and that sea-ice cover was greater and the AO more negative in the early and late 19th century compared to the 20th.